Expandable push-in arcuate interbody spinal fusion implant with tapered configuration during insertion

ABSTRACT

A push-in interbody spinal fusion implant having an expandable height and having an at least in part frusto-conical shape or a shape of cylinder split along a horizontal plane through its mid-longitudinal axis with an upper member and a lower member angled to each other during insertion into the spine.

[0001] This application is a continuation of application Ser. No.09/772,309, filed Jan. 29, 2001, which claims the benefit of provisionalApplication No. 60/180,404, filed Feb. 4, 2000, which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to an improved push-ininterbody (for placement at least in part between adjacent vertebralbodies) spinal fusion implant for the immobilization of vertebrae. Thepresent invention is directed to push-in implants only and not tothreaded implants. In particular, the invention relates to a push-inspinal fusion implant that is selectively directionally expandable andwhich specifically has height raising capabilities that are utilizedonce the implant is initially positioned. More particularly, theinvention relates to a push-in implant having arcuate portions of upperand lower members that in a first, collapsed, or insertion position areangled to one another and form at least a portion of a frusto-conicalshape, or of a cylinder split along a horizontal plane through itsmid-longitudinal axis wedging the upper half from the lower half by aninclined plane, along a substantial portion of the length of theimplant.

[0004] 2. Description of the Related Art

[0005] Push-in spinal fusion implants having upper and lower arcuateportions adapted for placement in contact with adjacent vertebral bodiesare known in the related art. Such a push-in spinal fusion implant wasinvented by Michelson and is disclosed in U.S. Pat. No. 5,593,409, filedFeb. 17, 1995, which is hereby incorporated by reference.

[0006] Lordotic, frusto-conical, or tapered, push-in spinal fusionimplants are also known in the art. By way of example, Michelson hasinvented such implants as disclosed in U.S. application Ser. No.08/484,928, filed Jun. 7, 1995, which is hereby incorporated byreference.

[0007] Expandable fusion implants are known in the related art. Thefirst expandable spinal fusion (allowing for the growth of bone fromvertebral body to vertebral body through the implant) implant wasinvented by Michelson and is disclosed in U.S. Pat. No. 5,776,199, filedJun. 28, 1988, which is hereby incorporated by reference.

[0008] Lordotic, frusto-conical, or tapered, spinal fusion implants havethe advantage of restoring or enhancing spinal lordosis. Push-in spinalfusion implants offer the advantage of being easily positioned in theimplantation space and of having excellent fastening or holdingfeatures. Expandable fusion implants offer the advantage of allowing forthe placement of a potentially larger implant through a smaller openingin a patient's body. Selective expansion along a single direction, (e.g.vertically only when correctly installed) offers the advantage ofincreasing the height of the implant and therefore the distraction ofthe disc space, but without a concomitant increase in the width of theimplant.

[0009] There exists a need for an artificial interbody spinal fusionimplant providing for all of the aforementioned advantages incombination.

SUMMARY OF THE INVENTION

[0010] In accordance with the present invention, as embodied and broadlydescribed herein, there is provided an expandable push-in artificialinterbody spinal fusion implant, having a shape that is generallyfrusto-conical or generally that of a cylinder split along a horizontalplane through its mid-longitudinal axis wedging the upper half from thelower half by an inclined plane when inserted, for insertion across adisc space between two adjacent vertebral bodies of a human spine. Thepush-in implant of the present invention includes an upper member havingan arcuate portion adapted for placement toward and at least in partwithin one of the adjacent vertebral bodies and a lower member having anarcuate portion adapted for placement toward and at least in part withinthe other of the adjacent vertebral bodies. The arcuate portions of theupper and lower members have at least one opening in communication withone another for permitting for the growth of bone from a vertebral bodyto an adjacent vertebral body through the implant. The upper and lowermembers are articulated therebetween, preferably proximate one of theproximal ends and the distal ends of the upper and lower members andpreferably allow for divergence between the articulating members at theend opposite the articulating end of the implant. The upper and lowermembers have a first position relative to one another that allows for acollapsed implant height and a second position relative to one anotherthat allows for an increased height. The arcuate portions of the upperand lower members in the first position of the present invention areangled to one another and form at least a portion of a frusto-conicalshape, or of a cylinder split along a horizontal plane through itsmid-longitudinal axis wedging the upper half from the lower half by aninclined plane, along the length of the implant. On the exterior of eachof the opposed arcuate portions of the upper and lower members is atleast one bone-engaging projection adapted for linear insertion forengaging the adjacent vertebral bodies. The upper and lower members havea leading or distal end, an opposite trailing or proximal end, and alength therebetween. A blocker that is preferably in the form of anexpander is located proximate at least one of the ends for holding atleast a portion of the upper and lower members apart so as to maintainthe increased height of the implant and resist the collapse of theimplant to the collapsed implant height. Expansion of the implantpreferably increases the implant height only, that is in a plane passingthrough the mid-longitudinal axis of the implant and the upper and lowermembers.

[0011] The blocker need not be in contact with the upper and lowermembers when the implant is initially inserted into the implantationspace. The blocker may be a block or any type of spacer that is insertedbetween or otherwise holds apart the articulated upper and lower membersafter the implant is positioned so as to hold portions of the upper andlower members spaced apart the optimal height and angulation relative toone another. That is, the implant may be expanded with an extrinsic tooland then the expanded portions held apart in the second position by athird body blocker or blockers placed therebetween. Further, a physicianmay be able to select from a series of blockers having different heightsusable with the same implant. The present invention includes expandingthe implant with a tool, such as a spreader or a distractor, but is notlimited to a scissors type, a rack and gear type, a threaded member typeor any other type of particular external expander tool mechanism. Eachtool nevertheless preferably engages the upper and the lower implantmembers to urge the implant apart. Then the blocker may be inserted intocontact with the upper and lower members to maintain the implant at anexpanded height. The height of the gap created by expanding the implantmay be measured so that the appropriately sized blocker or expander maybe inserted into contact with the upper and lower members depending uponthe amount of distraction of the implant desired by the physician.

[0012] In a preferred embodiment, the blocker is in contact with theupper and lower members prior to the implant expansion, and the blockeris itself the expander, which may be operated by an extrinsic tool. Byway of example only, the expander may rotate: to increase the height ofthe implant; in a single direction; more than 40 degrees and less than140 degrees and more preferably approximately 90 degrees to move from afirst insertion position to a second/deployed position; and in a planeperpendicular to the longitudinal axis of the implant to increase theheight of the implant. The expander preferably remains in the sameperpendicular plane relative to the longitudinal axis of the implantwhen rotated. In another embodiment the expander may be a member, suchas a plate, a rod, or of any other configuration suitable for theintended purpose initially within the interior between the upper andlower members in a collapsed position that is erected to a more erectposition when the implant is in the expanded position. The expander canbe hollow or solid.

[0013] In a preferred embodiment, the expander preferably has meansincluding, but not limited to, an opening, a projection, or a detentadapted to cooperatively engage a tool used to rotate the expander toincrease the height of the implant. The opening, projection, or detentis adapted to cooperatively engage a tool that preferably rotates aboutan axis parallel to the longitudinal axis the implant to rotate theexpander to increase the height of the implant. Rather then having anopening, a projection, a detent, or a central aperture, the expander mayhave two or more recesses or holes placed on or through the proximalface to engage a tool. In an alternative embodiment of the expander,cutouts may be positioned along a portion of the perimeter of theexpander.

[0014] The expander is preferably located proximate at least one of theproximal end or the distal end of the upper and lower members. Theexpander, however, need not be so located. The expander may be spacedaway from the end and even permit a hollow portion to exist on both theproximate and distal sides of the expander. The upper and lower memberspreferably have an interior surface therebetween and a hollow definedtherein with the expander located proximate one of the longitudinal endsof that interior hollow. The hollow between the ends of the upper andlower members is preferably unobstructed by the expander so as to permitgrowth of bone directly through the hollow unobstructed by the expanderfrom vertebral body to vertebral body through the implant transverse tothe longitudinal axis of the implant. The implant may comprise a secondand lesser hollow extending at least in part from the expander to theend of the upper and lower members proximate that expander. A preferredexpander mechanism includes an expander in combination with cooperatingsurfaces of the end wall of the implant that guide and support theexpander.

[0015] Preferred forms of interbody spinal fusion implants have asubstantial hollow portion. Certain expandable interbody spinal fusionimplants that increase in height only of the related art contain anexpansion mechanism passing longitudinally therethrough or an expansionmechanism that is configured for movement of the expansion mechanismfrom proximate one end of the hollow portion to proximate the other endof the hollow portion, thus requiring the expander to pass through thelength of the hollow portion. A preferred embodiment of the presentinvention overcomes these limitations.

[0016] The expander moves the arcuate portions of the upper and lowermembers from an angled orientation to a parallel orientation relative toone another; from a first angled orientation to a second angledorientation relative to one another; or from a first height at each endto a second and greater height at at least one and possibly both ends,but in each event the arcuate portions of the upper and lower members inthe first or insertion position are angled to one another over asubstantial portion of the length of the implant, and/or form at least aportion of a frusto-conical shape, or of a cylinder split along ahorizontal plane through its mid-longitudinal axis wedging the upperhalf from the lower half by an inclined plane, along the length of theimplant. Each of the upper and lower members may structurally cooperatewith a blocker, or expander so as to keep it located so as to functionfor its intended purpose. By way of example, each of the upper and lowermembers preferably has a track within which the blocker may be capturedor the expander rotated. The tracks may be configured to permit theexpander to rotate therein and then to move from side to sidetherewithin. The track of the upper member and the track of the lowermember are preferably in the same plane and the plane is preferablyperpendicular to the longitudinal axis of the implant.

[0017] A preferred expander has a first height in a first or insertionposition and a greater second height when rotated or positioned into asecond or deployed position to increase the maximum height of theimplant from a first maximum height to a second maximum height. By wayof example, at least one of the tracks of the upper and lower memberspreferably has a cooperating surface and the expander has acorresponding cooperating surface that contacts the cooperating surfaceof the track to orient the expander in a predetermined position. Thecooperating surfaces preferably orient the expander within the implantsuch that the axis of rotation of the expander is parallel with thelongitudinal axis of the implant and, more preferably, center theexpander within the implant such that the axis of rotation of theexpander coincides with the longitudinal axis of the implant. As may beadvantageous for the further loading of the implant withfusion-promoting material, the expander may cooperate with the trackingsurfaces of the upper and lower members to allow the expander to slidefrom side-to-side for easier access to the implant interior.

[0018] The implant is preferably packed full of bone or otherfusion-promoting substances prior to expansion of the implant. Expansionof the implant results in a space being formed in the implant interiorinto which additional fusion promoting substances such as bone maypreferably be packed. Rotating the expander within the implant causes avoid that can be filled with bone. If the expander is configured topermit side-to-side movement, then packing of additional bone into theimplant is easy.

[0019] When installing a preferred implant from the posterior approachto the spine, the implant is driven from the trailing end and theexpander is at the leading end at the anterior aspect of the spine. Whenexpanded, the implant installed from the posterior aspect leaves a voidat the leading end of the implant near the anterior aspect of the spinebecause the leading end of the implant has been made taller, the voidpreferably being packed with bone. Additionally, the path left behind inthe bone filled interior of the implant by the tool used to access theexpander through the bone filled interior to position the expander ispreferably packed with bone as well.

[0020] In a preferred embodiment of the present invention, the expanderheight change from the first position to the second position correspondsto substantially the same change in height of the implant along at leasta portion of the length of the implant. The expander may be configuredin different ways. A preferred configuration for a rotational expanderincludes: a first dimension corresponding to the width of the expanderwhen the implant is initially inserted into the spine and to the heightof the rotational expander when the rotational expander is rotated toincrease the height of the implant; and a second dimension correspondingto the height of the expander when the implant is initially insertedinto the spine and to the width of the expander when the expander isrotated to increase the height of the implant. The first dimensionpreferably is greater than the second dimension.

[0021] The expander may have an upper surface, a lower surface, and sidesurfaces as defined when the expander is positioned after rotation toincrease the height of the implant. As used herein, the term “sidesurfaces” refers to those portions of the expander that extend from theupper member to the lower member after the expander has been rotatedinto its second or deployed position to increase the height of theimplant. The “upper” and “lower” expander surfaces refer to thoseportions of the expander that are in contact with the upper and lowermembers when the implant is in its second or expanded configuration.Each of the upper and lower surfaces of the expander may lie generallyin a plane and may be generally parallel to one another. The sidesurfaces and the upper and lower surfaces may be oriented so as tosubstantially form a parallelogram, which will typically be in the shapeof a rectangle generally.

[0022] A preferred expander is in the form of a modified rectangle orrhomboid. The expander generally has a longer dimension and a shorterdimension. When the expander is in a first position, the short dimensionspans the distance between the upper and lower members and when theexpander is in the second position, the expander's long dimension spansthe distance between the upper and lower members.

[0023] The expander may have a cross-section with the side surfacesintersecting the upper and the lower surfaces at junctions, which may betwo diametrically opposed corners and two diametrically opposed arcs.The two diametrically opposed arcs may be each of the same radius and,preferably, the diagonal or modified hypotenuse “MH” between the opposedarcs has a maximum dimension that generally approximates the distancebetween the upper and lower surfaces such that, when the expander isrotated from a first insertion position toward a second/deployedposition, no substantial over-distraction occurs between the adjacentvertebral bodies as would occur if the height of the implant wasincreased markedly beyond that obtained in the second/deployed position.The two diametrically opposed corners may form a 90-degree angle. Theexpander preferably has a fixed shape during movement from a firstinsertion position to a second/deployed position within the implant.

[0024] In a preferred embodiment, a modified hypotenuse or diagonal “MH”is the dimension between the two diametrically opposed arcs that allowsfor the rotation of the expander from a first position to a secondposition without substantial over-distraction occurring during thisprocess. The phrase “without substantial over-distraction” is defined asdistracting the vertebral bodies in the range of elastic deformation andshort of plastic deformation and tissue failure. To avoid any ambiguityregarding the phrase “without over-distraction,” this phrase and theindividual words contained therein are not being used as they may be intheir normal or ordinary use, but are being used as defined in thisapplication only. In the example of this rotational expander, the MHcould be identical in length to the height thereby assuring literally nooverdistraction. It may be preferred, however, to have the MH justslightly greater in length than the height to insure the stability ofthe expander in the expanded or second position because this would thenrequire additional force over the stable position to derotate theexpander.

[0025] In accordance with an embodiment of the present invention, asecond expander may be located between the upper and lower members formoving at least a portion of the upper and lower members away from oneanother to increase the height of the implant as defined by the maximumdistance between the arcuate portions of the upper and lower membersproximate that expander. All of the features described herein for theexpander may also be applicable to the second expander. Additionally,the second expander may be located proximate an end of the implantopposite the other expander, thereby providing an implant capable ofbeing expanded at both ends of the implant. The increased height of theimplant resulting from moving the two expanders may be constant orvaried along the length of the implant according to the desiredconfiguration of the implant and the relative dimensions of theindividual expanders. A given implant may be adapted to receive orcooperatively engage a series of progressively sized (taller) blockersor expanders to allow the surgeon to make a final height selection atthe time of surgery.

[0026] In accordance with an embodiment of the present invention, theimplant may include an expansion mechanism including the expander and atleast one partial wall structure preferably located proximate an implantend that guides and holds the expander in a predetermined position.

[0027] The implant may have an overlapping step-cut wall junctionbetween the upper and lower members, which offers as some of itsadvantages: increasing the lateral rigidity of the implant, holding theimplant in the closed first position until expanded, and to the extentdesired retaining the fusion-promoting materials within the implant. Thewall junction may be either solid or perforated.

[0028] One of the upper and lower members preferably has an interiorwall extending toward the other of the upper and lower members and, morepreferably, has two interior walls extending from each side of thearcuate portion. The interior walls may be aligned parallel with thelongitudinal axis of the implant. The other one of the upper and lowermembers preferably has an interior-contacting surface adapted to contactor receive the interior longitudinal wall.

[0029] By way of example, one of the upper and lower members may have alongitudinally extending interior wall, which is preferably unexposed,extending toward the other of the upper and lower members when theimplant is in an initial insertion position. When the implant is in thefinal expanded or deployed position the implant has a preferred shapesuch that each of the arcuate portions of the upper and lower membersare separated by at least a portion of interior wall, which in thisposition preferably has an exposed side.

[0030] The upper and lower members in certain embodiments arearticulated to one another so one of the respective ends of the upperand lower members remain articulated while the other of the respectiveends of the upper and lower members are free to move away from oneanother. In a preferred embodiment, the articulating means is achievedwithout a third member, such as an axle shaft, for example, passingthrough the implant. The articulating means preferably is formed intothe implant walls themselves, and in a further preference in such a waythat the two-implant halves may be articulated when at 90 degrees toeach other. The halves then are moved, much like a book closing, towardeach other prior to insertion into the implantation space in the spine.Once the upper and lower members are closed from the approximately 90degrees articulating position, much like closing the leaves of a book,the upper and lower members of the implant are locked together at thearticulation so that the members will not disarticulate when in use.Other types of articulation as would be known to one of ordinary skillin the art are within the scope of the present invention.

[0031] By way of example, the upper and lower members preferably have acooperating rotational articulation or pivot point between a proximateone of the proximal end and the distal end of the upper and lowermembers. The cooperating rotational articulation preferably is proximateone of the proximal end and the distal end of the upper and lowermembers at an end opposite the expander when only one end is to beexpanded. A preferred rotational articulation configuration includescooperating brackets and projections configured such that articulationtherebetween occurs when the upper and lower members are substantiallyperpendicular to one another. Such a configuration offers the advantagethat the brackets and the projections will not disengage one anotherwhen articulated for use such as insertion into the spine and subsequentexpansion within a range of movement of the upper and lower membersresulting from the expander positioning.

[0032] When the implant is in the final or expanded position the implantmay take the general form of a frusto-conical shape split along ahorizontal plane through its mid-longitudinal axis with the upper halfand the lower half wedged apart by an inclined plane or of a cylindersplit along a horizontal plane through its mid-longitudinal axis withthe upper half and the lower half wedged apart by an inclined plane.

[0033] At least one and preferably both of the upper and lower membersmay have a screw hole passing through the trailing end, which preferablyis adapted to receive a screw passing through the end of the upper andlower members and from the interior of the implant into each of theadjacent vertebral bodies to anchor the implant, further stabilize thosevertebral bodies relative to each other, prevent undesirable motion atthe vertebral body implant interfaces, increase the compressive load atthe implant trailing end, prevent rocking and thereby to mitigateagainst excessive peak loads, and to more uniformly distribute loadsimparted to the implant over the length of the implant to the adjacentvertebral bodies. The implant may have a side configured, when in theexpanded position, to cooperate with another interbody spinal fusionimplant so as to allow the pair of implants to have a reduced combinedwidth.

[0034] The trailing end of the implant preferably has a tool-engagingportion, but the implant may be adapted to cooperatively engage a driverat another location or by any means as would be known to one of ordinaryskill in the art. This tool-engaging portion is adapted to engage aninsertion tool that holds the implant during insertion into position inthe spine. The configuration of the tool-engaging portion may be anopening, and more particularly an opening that is along the longitudinalaxis of the implant. It is appreciated that the tool-engaging portionneed not be an opening. A hole or a blind hole, threaded or otherwise,is preferred in another embodiment. In another preferred embodiment theopening preferably is a threaded slot that functions to cooperativelyengage and disengage a tool for use in inserting the implant. Inspecific embodiments, the leading or trailing end may have wallportions, and/or be adapted to cooperatively engage a cap. Either theend wall portions or a cap may have an opening or openings that mayfunction to hold fusion-promoting materials within the implant and/or,permit vascular access and bone growth therethrough.

[0035] For an embodiment of an implant of the present invention havingone expander, the main access opening is preferably at the end oppositefrom the expander. The main opening may be at either the distal orproximal end of the implant. The end of the upper and lower memberscontaining the expander may serve as a secondary access opening.

[0036] By way of example, an implant configured for insertion from ananterior approach may be initially packed from the distal or leading endof the implant. The implant is then driven into position. Once theexpander is moved into final position and any associated tool forpositioning the expander is withdrawn from the expander, any void in thebone packed into the implant interior may be filled. The expander may bemoved from side-to-side to pack more bone into the implant. In essence,the side-to-side movement of the expander provides for a secondaryaccess opening for accessing the hollow interior of the implant and forcompressively loading it with fusion-promoting substances. Theaccompanying drawings, which are incorporated in and constitute a partof this specification, are by way of example only and not limitation,and illustrate several embodiments of the invention, which together withthe description, serve to explain the principles of the invention. Thescope of the invention is limited only by the scope of the claims asfrom the present teachings other embodiments of the present inventionshall be apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is an exploded perspective view of a spinal fusion implantof one embodiment of the present invention;

[0038]FIG. 1A is a perspective view of an alternative embodiment of ablocker in the form of an expander for use with the spinal fusionimplant of FIG. 1;

[0039]FIG. 1B is a perspective view of another alternative embodiment ofa blocker for use with the spinal fusion implant of FIG. 1;

[0040]FIG. 1C is a perspective view of yet another alternativeembodiment of a blocker for use with the spinal fusion implant of FIG.1;

[0041]FIG. 2 is a top plan view of the implant of FIG. 1;

[0042]FIG. 2A is a top plan view of an alternative embodiment of thepresent invention;

[0043]FIG. 3 is a trailing end view of the implant of FIG. 1;

[0044]FIG. 3A is a trailing end view of the implant of FIG. 2A;

[0045]FIG. 3B is a trailing end view of yet another alternativeembodiment of the present invention;

[0046]FIG. 4 is a side elevation view of the implant of FIG. 1;

[0047]FIG. 4A is a side elevation view of the implant of FIG. 2A;

[0048]FIG. 5 is a leading end view of the implant with the end cap thereattached of FIG. 1;

[0049]FIG. 5A is a leading end view of the implant of FIG. 2A with anend cap attached;

[0050]FIG. 6 is a cross-sectional view along line 6-6 of FIG. 2;

[0051]FIG. 7 is a cross-sectional view along line 7-7 of FIG. 5;

[0052]FIG. 8 is a side elevation view of an end cap for use with theimplant of FIG. 1;

[0053]FIG. 9 is a schematic representation of a geometric configurationof a cross-section of an expander in accordance with one embodiment ofthe present invention;

[0054]FIG. 10 is a trailing end perspective view of the implant of FIG.1,

[0055]FIG. 11 is a side view of the implant of FIG. 10 being insertedfrom a generally anterior approach to the spine into an implantationsite formed across a disc space and two adjacent vertebral bodies of thespine shown in partial cross-section;

[0056]FIG. 12A is a cross-sectional view of the implant of FIG. 1inserted in an implantation site formed across the disc space and twoadjacent vertebral bodies of the spine;

[0057]FIG. 12B is a cross-sectional view of the implant of FIG. 1inserted in an implantation site of FIG. 12A and expanded to place theadjacent vertebral bodies in proper lordosis;

[0058]FIG. 12C is a trailing end perspective view of the implant of FIG.1 with the implant in an expanded position;

[0059]FIG. 13 is a trailing end view of the anterior aspect of twoadjacent vertebral bodies and two implants of FIG. 1 implantedtherebetween in a final position;

[0060]FIG. 13A is a trailing end view of the anterior aspect of twoadjacent vertebral bodies and two alternative embodiment implantsimplanted therebetween in a final position;

[0061]FIG. 14 is a cross-sectional side view of an implantation siteformed posteriorly across the disc space between two adjacent vertebralbodies and a second embodiment of an implant of the present inventionfor posterior insertion being installed into the implantation site;

[0062]FIG. 14A is a side view of an alternative variation of a secondembodiment of the implant of FIG. 14 for posterior insertion;

[0063]FIG. 15 is a cross-sectional side view of the implantation siteformed across the space between two adjacent vertebral bodies and theimplant of FIG. 14 installed into the implantation space;

[0064]FIG. 16 is a leading end view of the implant of FIG. 14;

[0065]FIG. 17 is a top plan view of another embodiment of the presentinvention inserted upon the lower vertebral body of an implantation siteformed anteriorly across a disc space with the vertebral body shown inpartial cross-section;

[0066]FIG. 18A is a cross-sectional side view of the implantation siteformed across the space between two adjacent vertebral bodies and one ofthe implants of FIG. 17 installed into the implantation space;

[0067]FIG. 18B is a trailing end view of the anterior aspect of twoadjacent vertebral bodies and the implant of FIG. 17 implantedtherebetween in an expanded position as well as another embodimentdesigned to be used as a side-by-side pair;

[0068]FIG. 19 is a cross-sectional side view of the implant of FIG. 18Awithout bone or other fusion-promoting substances shown therein for thepurpose of illustrating a preferred configuration for articulating theupper and lower members together with a hook and peg configuration thatprevents the implant from over expanding and with an alternative secondhook and peg shown on the right hand side of the figure in dashed lines;

[0069]FIG. 20 is a partial cross sectional view of an embodiment of aninterlocking wall design along line 21-21 of FIG. 19;

[0070]FIG. 21 is a partial cross sectional view of another embodiment ofan interlocking wall design along line 21-21 of FIG. 19;

[0071]FIG. 22A is a cross-sectional side view of an alternativeembodiment of an implant of the present invention with a pivotingtrailing end that is also a blocker in the trailing end in the openposition;

[0072]FIG. 22B is a cross-sectional side view of an alternativeembodiment of an implant of the present invention with a pivotingtrailing end that is also a blocker with the trailing end in the closedposition; and

[0073]FIG. 23 is a trailing end perspective view of the implant of FIG.22B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0074] The following description is intended to be representative onlyand not limiting and many variations can be anticipated according tothese teachings, which are included within the scope of this inventiveteaching. Reference will now be made in detail to the preferredembodiments of this invention, examples of which are illustrated in theaccompanying drawings.

[0075] Shown in FIGS. 1, 2, 3, 4, 5, 6, 7, and 10-13, in accordance withthe present invention, as embodied and broadly described herein, is oneembodiment of an expandable push-in artificial interbody spinal fusionimplant 100 for anterior insertion across a disc space D between twoadjacent vertebral bodies V of a human spine. Push-in implant 100 of thepresent invention includes an upper member 102 having an arcuate portion104 adapted for placement toward and at least in part within the upperof the adjacent vertebral bodies V and a lower member 106 having anarcuate portion 108 adapted for placement toward and at least in partwithin the lower of the adjacent vertebral bodies V. Arcuate portions104, 108 of upper and lower members 102, 106 have at least one opening110, 112 in communication with one another for permitting for the growthof bone from vertebral body V to adjacent vertebral body V throughimplant 100. Upper and lower members 102, 106 are articulatedtherebetween at an adjacent one of the proximal ends and the distal endsof upper and lower members 102, 106 and allow for rotation between thearticulating members at the end opposite the articulating end of implant100. Upper and lower members 102, 106 have a first position relative toone another that allows for a collapsed implant height and a secondposition relative to one another that allows for an increased height.Arcuate portions 104, 108 of upper and lower members 102, 106 in thefirst position of the present invention are angled to one another andform at least a portion of a frusto-conical shape along the length ofimplant 100. On an exterior 120 of each of opposed arcuate portions 104,108 of upper and lower members 102, 106 is a portion 114, 116 of atleast one bone-engaging projection 118 adapted for linear insertion,which in one preferred embodiment is a ratchet.

[0076] Preferred embodiments of the present invention illustrated in theattached figures and discussed herein have arcuate portions 104, 108angled to one another to form at least a portion of a frusto-conicalshape along the length of implant 100. Alternatively, the arcuateportions may form at least a portion of a shape described as a cylindersplit along a horizontal plane through its mid-longitudinal axis withthe upper half and the lower half wedged apart by an inclined plane orany variation thereof suitable for the intended purpose of theexpandable, push-in, non-threaded implant having upper and lower arcuateportions of the present invention.

[0077] While a specialized form of a blocker 121 is described insignificant detail below with reference to expander 122, blocker 121need not be in contact with upper and lower members 102, 106 whenimplant 100 is initially inserted into the implantation space. Blocker121 may be a block or any type of spacer that is inserted between thearticulated upper and lower members 102, 106 after implant 100 ispositioned so as to hold portions of the upper and lower members 102,106 spaced apart the optimal height and angulation relative to oneanother. That is, the implant may be expanded with an extrinsic tool andthen the expanded portions held apart in the second position by a thirdbody blocker placed therebetween. Further, a physician may be able toselect from a series of blockers having different heights usable withthe same implant. The present invention includes expanding the implantwith a tool, such as a spreader or a distractor but is not limited to ascissors type, a rack and gear type, a threaded member type or any otherspecific type of movement mechanism. Each tool nevertheless preferablyengages upper and lower implant members 102, 106 to urge them apart.Blocker 121 is then inserted into contact with upper and lower members102, 106 to maintain implant 100 at an expanded height. The height ofthe gap created by expanding implant 100 may be measured so that theappropriately sized blocker 121 or specialized blocker, expander 122,may be inserted in implant 100 depending upon the amount of distractionof implant 100 desired by the surgeon.

[0078] Blocker 121 that is preferably in the form of expander 122 islocated proximate at least one of the ends of the implant upper andlower members 102, 106 and holds at least a portion of upper and lowermembers 102, 106 apart so as to maintain the increased height of implant100 and resist the collapse of implant 100 to the collapsed implantheight. Expander 122 in the present embodiment increases the implantheight as measured in a plane passing through the mid-longitudinal axisof implant 100 and upper and lower members 102, 106 during positioningof expander 122 and as may be desirable is capable of selectivelyincreasing the height of the implant only.

[0079] Expander 122 in the present embodiment is adapted to rotate in asingle direction approximately 90 degrees to move from an initial(first) insertion position 1, as best shown in FIGS. 1, 3 and 10, to afinal (second) deployed or expanded position F, as best shown in FIGS.13 and 13A, to increase the maximum height H of implant 100. Expander122 preferably rotates in a plane perpendicular to the longitudinal axisL of implant 100 to increase the maximum height H of implant 100. Duringrotation, expander 122 remains in the same perpendicular plane relativeto the longitudinal axis L of the implant. It is appreciated that anexpander within the scope of the present invention may be designed to:rotate in either direction or both directions; rotate more than 40degrees and less than 140 degrees; rotate more or less than 90 degrees;or rotate in a plane other than perpendicular.

[0080] Expander 122 has an opening 124 adapted to cooperatively engage atool (not shown) used to rotate expander 122 to increase height H ofimplant 100. Opening 124 is adapted to cooperatively engage a tool thatpreferably rotates about an axis parallel to the longitudinal axis L ofimplant 100 to rotate expander 122 to increase height H of implant 100.Opening 124 also may be used as a passageway to pass fusion-promotingsubstances through expander 122 and into implant 100. It is appreciatedthat the expander may also include a projection, a detent, or any otherconfiguration in place of or in addition to an opening so as tocooperatively engage a tool to move the expander.

[0081] In an alternative embodiment, an expander 122′ could have cutoutsalong any portion of its perimeter not involved in the actual rotationas shown in FIG. 1A. In another alternative embodiment, a blocker 121having cutouts along a portion of its perimeter can be positioned intothe implant as shown in FIG. 1B. The cutouts can be used to engage araised area within the implant to lock blocker 121 or expander 122′ intoposition or be used by the surgeon to grasp blocker 121 with a tool thatcooperatively engages the cutouts to facilitate inserting blocker 121into the implant. Rather then having an opening, a projection, a detent,or a central aperture, a blocker 121′ alternatively could have two ormore recesses or holes placed on or through the proximal face to engagea tool as shown in FIG. 1C.

[0082] As shown in FIGS. 1, 6, 7, 10, 12A-12C, and 13, in one preferredembodiment of the present invention for anterior insertion, expander 122is located proximate the trailing end 126 of upper and lower members102, 106. Three other preferred embodiments of the present invention foranterior insertion are shown in FIGS. 2A, 3A, 4A, and 5A, and in FIG.3B, and in FIG. 13A, respectively. While in another embodiment shown inFIGS. 14-16 for posterior insertion, expander 222 is located proximatethe leading end 250. As shown if FIGS. 17-19, in three more alternativeembodiments of the present invention for anterior insertion and possibleuse together, expanders 322 are located proximate each of leading andtrailing ends 330, 326 of implants 300.

[0083] Implant 100 preferably has an interior surface 128 and a hollow130 defined therein. Expander 122 of the present embodiment is locatedproximate interior surface 128 and more particularly proximate interiorsurface 128 at trailing end 126 of upper and lower members 102, 106. Asis preferred, hollow 130 between the ends is unobstructed by expander122 so as to allow for the unimpeded loading of the interior of theimplant with the desired fusion-promoting substances; thus, loading theimplant is easy. Further, this preferred configuration of implant 100makes available all of the volume of the hollow to containfusion-promoting substances and so as to permit for the growth of bonedirectly through the hollow unobstructed by the expander to adjacentvertebral bodies V. Unobstructed hollow 130 further allows for packingimplant 100 with fusion-promoting substances. It is appreciated thatdepending on the intended results, the expander also may be located atdistal end 126 or leading end 150 of upper and lower members 102, 106 oranywhere else within the implant. The unobstructed hollow preferably hasno mechanism extending along the longitudinal axis of the implant whenfinally deployed and the mechanism that moves the implant from a firstposition to a second position preferably does not move expander 122longitudinally through the hollow portion. The expander may work bypivoting on a surface in contact with an interior wall portion of atleast one of the upper and lower members 102, 106. Moreover, multipleexpanders may be used in contact with upper and lower members 102, 106at any location within the implant.

[0084] An alternative embodiment of an expander used with the presentinvention includes an expander having an external thread that cooperateswith converging threaded portions of the upper and lower members 102,106 to expand the implant as the expander is rotated into position.Another alternative embodiment of an expander includes an expanderhaving a cam configuration to expand the implant upon rotation.

[0085] The mechanism or tool used to move the expander is not part ofthe implant itself as the mechanism or tool is removed from the implantupon moving the expander, e.g. such as to rotate it into place and thusexpand the implant to the final expanded position.

[0086] Expander 122 of the present embodiment moves arcuate portions104, 108 of upper and lower members 102, 106 from a first angledorientation A as shown in FIGS. 1 and 11 in a first position, to asecond angled orientation A′ as shown in FIG. 12B where implant 100 hasa generally oblong cross section at trailing end 126, in a secondposition. The implant need not be a true frusto-conical shape as a crosssection need not form a complete circle, but may have portions of theperimeter absent, less round, flattened, flattened in more than onelocation including on two or more sides, or other. It is appreciatedthat the expander also may move the arcuate portions of the upper andlower members from a first height at each end to a second and greaterheight at each end.

[0087] In this embodiment, each of upper and lower members 102, 106structurally cooperate with expander 122 so as to keep it located so asto function for its intended purpose. Each of upper and lower members102, 106 of the implant of FIG. 1 has a track 132, 134 within whichexpander 122 rotates. As best shown in FIGS. 1 and 13, track 132, 134 isconfigured to permit expander 122 to rotate therein and then to movefrom side to side within track 132, 134. Track 132 of upper member 102and track 134 of lower member 106 are in the same plane and the plane isperpendicular to the longitudinal axis of implant 100. It is appreciatedthat the track of the upper and lower members may be in differentplanes. Such a track design may be used with an expander with a step init or with offset tabs to engage tracks in different planes than oneanother. As with the expander, the tracks also may be at various anglesto the longitudinal axis of the implant including parallel with thelongitudinal axis of the implant. Other means for respectively engagingthe implants and the expander position thereof are anticipated andwithin the scope of the present invention.

[0088] In rotating the expander, the longer dimension of the expander issubstituted for the lesser dimension of the expander thuscorrespondingly increasing the maximum height of the implant from thefirst to the second position. As best shown in FIG. 9, the schematicrepresentation of a geometric configuration of a cross-section of anexpander 122 in accordance with one embodiment of the present invention,includes: a first dimension X corresponding to the height of expander122 when implant 100 is initially inserted into the spine and to thewidth of expander 122 when expander 122 is rotated to increase height Hof implant 100; and a second dimension Y corresponding to the width ofexpander 122 when implant 100 is initially inserted into the spine andto the height of expander 122 when expander 122 is rotated to increaseheight H of implant 100. Second dimension Y is greater than firstdimension X. Expander 122 has an upper surface 136, a lower surface 138,and side surfaces 140 as defined when expander 122 is positioned afterrotation to increase height H of implant 100. As used herein, the term“side surfaces” refers to those portions of expander 122 that extendfrom upper member 102 to lower members 106 after expander 122 has beenrotated into its final deployed, or second position to increase theheight H of implant 100. The “upper” and “lower” surfaces refer to thoseportions of expander 122 that are in contact with upper and lowermembers 102, 106 when implant 100 is in its second position andconfiguration and is fully expanded.

[0089] A preferred expander 122 is in the form of a modified rectangleor rhomboid. The expander generally has a longer dimension Y and ashorter dimension X. When the expander is inserted into a firstposition, the short dimension X spans the distance between upper to thelower members 102, 106 and when expander 122 is in the second position,the longer dimension Y of expander 122 spans the distance between upperand lower members 102, 106.

[0090] Expander 122 in one embodiment of the present embodiment has across-section with side surfaces 140 intersecting upper and lowersurfaces 136, 138 at two junctions which may be diametrically opposedcorners 142 and two diametrically opposed arcs 144. Arcs 144 arepreferably each of the same radius and the modified hypotenuse MHbetween opposed arcs 144 generally approximates the distance betweenupper and lower surfaces 136, 138 such that, when expander 122 isrotated from an initial insertion position toward a final deployedposition, no substantial over-distraction occurs between adjacentvertebral bodies V.

[0091] The modified hypotenuse MH of this embodiment of the presentinvention may be equal, slightly less than, or slightly greater thandimension Y of expander 122. Having the modified hypotenuse MH beslightly greater than the dimension Y offers the advantage of havingexpander 122 stabilized by an over-center position, such that moreenergy would be required to derotate the expander than for it to remainin the deployed or second position. By “without substantialover-distraction” what is meant is that the modified hypotenuse MHlength is closer to the expander dimension Y than to the unmodifiedhypotenuse UH; and is selected to allow the implant to preferablyoperate in the range of elastic deformation of the tissues about theoperated disc space. Corners 142 may form, but not necessarily, a90-degree angle and have an unmodified hypotenuse dimension UH.

[0092] By way of example, consider one embodiment of expandable implant100 of the present invention having an optimum expanded height of 18 mmfor a given implantation space. Any implant bigger than 18 mm should notbe used in this implantation space because during expansion of theimplant, its height would move through the range of elastic deformationof the surrounding tissues and after that the implant would crush thevertebral bone or tear ligaments. Inserting an expander such that whenthe implant is fully expanded allows the implant to be 18 mm would beideal. It may be that an implant having a 17.5 mm expanded height forthis implantation space is nearly as good, but a 16 mm expanded heightmay be too short to fit tightly within the implantation space. Using apreferred rectangular expander without any modification to thehypotenuse that is adapted to expand the implant to the optimum 18 mmfinal height would require the expander to have a hypotenuse causing theimplant to exceed the 18 mm expanded height temporarily during rotationof the expander. So turning the expander without a modified hypotenusewould break the vertebrae or tear the ligaments. In reverse, if onecould not expand the implant to more than 18 mm without causing damageto the spine, then an implant selected to have an expander having a fullunmodified hypotenuse so as to upon rotation temporarily cause theimplant height to be 18 mm would in the finally expanded position allowthe implant height to collapse such that there would be insufficientheight for the implant to adequately distract the implantation space.Generally, the modified hypotenuse of the expander is closer in lengthto dimension Y of the expander than to the unmodified hypotenuse.

[0093] As best shown in FIG. 1 in this particular embodiment, expander122 has a depth dimension Z that is less than that of first and seconddimensions Y, X. Expander 122 of the present embodiment has a fixedshape during movement from initial insertion position I to finaldeployed position F within implant 100.

[0094] As shown in FIGS. 22A, 22B, and 23, blocker 121 may also take theform of a trailing wall that articulates or hinges to the inside ofimplant 100. The trailing wall may be left open during insertion ofimplant 100 so as to trail behind the upper and lower members. Thetrailing wall preferably does not protrude outside of a projectionrearward of the circumference of implant 100. Such a configurationpermits insertion of push-in implant 100 through a guard or tube adaptedto permit passage of the implant having a known circumference. Onceimplant 100 is implanted into position, the trailing wall is rotatedabout one of its ends and pushed into position and locked into place.This may occur by having the trailing wall contact an inclined planethat leads up to a notch into which the trailing wall locks into place.The trailing wall itself may also have at least one opening in it topermit the further loading of fusion-promoting materials into implant100. Blocker 121 may also be adapted to cooperatively engage a tool usedto move the blocker from an initial position to a final position toincrease the height of implant 100, the tool being removable aftermoving blocker 121 into the final position.

[0095] Implant 100 may be configured to have a rotational articulationbetween the upper and lower members adjacent one of the ends of theupper and lower members. The rotational articulation may be formed bythe upper and lower members interdigitating so as to cooperativelyengage. The rotational articulation may be configured so that engagementoccurs when the upper and lower members are substantially perpendicularto one another. The rotational articulation may also be configured toremain engaged within a range of movement of the upper and lower membersresulting from positioning implant 100 between a first position of theupper and lower members relative to one another allowing for a collapsedimplant height and a second position relative to one another allowingfor an increased implant height.

[0096] At least one or both of the upper and lower members of implant100 may be configured to have a screw hole passing therethrough that isadapted to receive a screw passing from an interior of implant 100 intoan adjacent vertebral body. The screw may be adapted to pass from theinterior of implant 100 through the screw hole and into the adjacentvertebral body to anchor implant 100 to the adjacent vertebral body.

[0097] Implant 100 may be configured to have a side surface contoured tocooperate with another implant when implant 100 is in a final position.Implant 100 and the cooperating implant may have a combined widththerebetween less than the combined height of implant 100 and thecooperating implant.

[0098] While modified hypotenuse MH is illustrated as being between arcs144 in this preferred embodiment, the configuration of expander 122 toform modified hypotenuse MH can take many forms, such that thosejunctions are relieved so as to have the desired lesser dimensiontherebetween, including arcs, chamfers, a series of angled surfaces, orany other shape so long as the modified hypotenuse MH is sufficientlyreduced in dimension to function for the intended purpose according tothe present teaching.

[0099] An embodiment of the present invention where modified hypotenuseMH is slightly greater than height Y offers the advantage of anover-center effect that locks expander 122 into place. In this instance,once expander 122 rotates past the diagonal of the modified hypotenuseMH, more force would be required to rotate it back from the finaldeployed position to its insertion position than in an embodiment wheremodified hypotenuse MH is equal to or less than height Y. Preferably,expander 122 offers a surgeon multiple sensory advantages including: thetactile feel of expander 122 going over center and locking into place;the visual of the handle of a tool rotating expander 122 such that thetool handle goes from perpendicular to parallel, the reverse, or other,to the disc space into place; and auditory from the sound of expander122 snapping into place.

[0100] Each of upper and lower surfaces 136, 138 of expander 122 of thepresent embodiment lie generally in a plane and are generally parallelto one another. For any implant it is anticipated that a physician maybe able to select from a series of blockers or expanders allowing forvarying the increase in the implant height. Side surfaces 140 and upperand lower surfaces 136, 138 are oriented so as to substantially form aparallelogram. Any of a number of configurations for the expander forincreasing the height of the implant is possible, based on the teachingsof the present application and such configurations as would be known toone of skill in the art are anticipated within the scope of the presentinvention.

[0101] The implant may preferably have an overlapping step-cut walljunction between upper and power members 102, 106 which offers theadvantage of increasing the lateral rigidity of implant 100 holding theimplant in the closed first position until expanded, and to the extentdesired retaining the fusion-promoting materials within. The walljunction may be either solid or perforated. As best shown in FIG. 1,upper member 102 in one embodiment of the preferred invention hasinterior walls 146 extending from each side of arcuate portion 104toward lower member 106. Interior wall 146 is aligned parallel tolongitudinal axis L of implant 100. Lower member 106 has aninterior-contacting surface 148 adapted to contact or receive interiorwall 146.

[0102] In a preferred embodiment, upper and lower members 102, 106 arearticulated to one another so one of the respective ends of upper andlower members 102, 106 remain articulated while the other of therespective ends of upper and lower members 102, 106 are free to moveaway from one another. In a preferred embodiment the articulating meansis achieved without a third member such as an axle shaft passing throughthe implant. The articulating means preferably is formed into theimplant walls themselves in such a way that the two implant halves maybe articulated when the halves are at 90 degrees to each other and thenthe halves are moved toward each other for insertion into theimplantation space in the spine. The two halves are closed much like thecover of a book. The halves are locked together such thatdisarticulation will not occur when the implant is assembled for use.Any of a number of ways of articulating or joining upper and lowermembers 102, 106 is possible.

[0103] As best shown in FIG. 1 in this embodiment, upper and lowermembers 102, 106 of the present embodiment have a pivot point betweenadjacent distal ends 126 or leading ends 150 of upper and lower members102, 106. The pivot point in the present embodiment is at the end ofimplant 100 opposite expander 122. The pivot point of the presentembodiment operates as a hinge or axle 152 but is formed out of thewalls themselves so as to preferably not intrude into the implantinterior or hollow or to block access thereto. Hinge 152 includes aprojection 154 extending radially from each side of arcuate portion 108of lower member 106 and a slotted bracket 156 extending from each sideof arcuate portion 104 of upper member 102 for engaging projection 154.Brackets 156 and projections 154 are configured such that engagementoccurs when upper and lower members 102, 106 are substantiallyperpendicular to one another. Brackets 156 and projections 154 areconfigured so as not to disengage within a range of movement of upperand lower members 102, 106 that would occur when the implant is in useeither during insertion or resulting from the expansion in height ofimplant 100.

[0104] As best shown in FIG. 11, interior wall 146 of upper member 102of the present embodiment is unexposed when implant 100 is in initialinsertion position 1. As shown in FIG. 12C, when implant 100 is in theexpanded position F, implant 100 has a shape such that each of arcuateportions 104, 108 of upper and lower members 102, 106 are separated byat least a portion of interior wall 146, which in this position has anexposed side. The exposed side of the present embodiment is smooth andflat.

[0105] As best shown in FIG. 8, a cap 158 having an exterior surface 160and an interior surface 162 is used to close leading end 150 of implant100. Interior surface 162 of cap 158 has spaced slots 164 about itscircumference to facilitate a snap fit between cap 158 and implant 100.Cap 158 and implant 100 can of course be adapted for either or both endsof implant 100.

[0106] As discussed above, implant 100 has a leading end 150 and atrailing end 126. One of the ends preferably has a tool-engagingportion. This tool-engaging portion is adapted to engage an insertiontool that holds implant 100 during insertion into position into thespine. The tool-engaging configuration may be an opening, and moreparticularly an opening that is along the longitudinal axis of theimplant. Of course, the tool-engaging portion need not be an opening. Ahole or a blind hole, threaded or otherwise, is preferred in anotherembodiment. In another preferred embodiment the opening preferably is athreaded slot that functions to cooperatively engage and disengage atool for use in inserting implant 100. The opening either alone on theproximal end of implant 100 or in conjunction with other openings on theproximal end function to hold fusion-promoting material in implant 100while permitting vascular access and bone growth through the opening oropenings.

[0107] Implants of the present invention may have an end adapted tocooperatively engage an implant driver. The anterior approach implantmay have a leading end, trailing end, or both ends that are adapted toengage a cap. One of the purposes for that cap includes restricting thepassage of fusion-promoting substances so that they remain loaded withinthe implant. Another purpose of the cap may be to add structural supportto the implant. The cap may be solid or it may have openingstherethrough. Any such openings could allow for the loaded material tostay within the implant while providing for vascular access to allow forthe ingrowth of blood vessels and the growth of bone through the end ofthe implant.

[0108] For a posterior approach implant, the cap may be on either orboth ends. The trailing end of the implant in a posterior approachimplant has direct exposure to the spinal canal where the spinal cordand nerve roots are located. A cap on a posterior approach implant maybe for the purpose of sealing off the spinal canal from thefusion-promoting substances contained in the hollow interior of theimplant so that no bone grows into the canal. Further, the presentinvention implant may be used in combination with chemical substancesand/or compounds applied at the trailing end of the implant to inhibitscar formation, and the cap may be of benefit in shielding thefusion-promoting substances contained in the implant from these scarformation inhibiting chemicals and compounds. It may also be for thepurposes identified herein used in association with the leading end capof an anterior approach implant.

[0109] Shown in FIGS. 2A, 3A, 4A, and 5A, in accordance with the presentinvention, as embodied and broadly described herein, is one embodimentof an expandable push-in artificial interbody spinal fusion implant 100′for anterior insertion across a disc space D between two adjacentvertebral bodies V of a human spine. Push-in implant 100′ includes anupper member 102′ having an arcuate portion 104′ adapted for placementtoward and at least in part within the upper of the adjacent vertebralbodies V and a lower member 106′ having an arcuate portion 108′ adaptedfor placement toward and at least in part within the lower of theadjacent vertebral bodies V. Arcuate portions 104′, 108′ of upper andlower members 102′, 106′ in a first position are angled to one anotherand form at least a portion of a frusto-conical shape along the lengthof implant 100′. On an exterior 120′ of each of opposed arcuate portions104′, 108′ of upper and lower members 102′, 106′ is a portion 114′, 116′of at least one bone-engaging projection 118 adapted for linearinsertion, which in one preferred embodiment is a ratchet.

[0110] Implant 100′ of FIGS. 2A, 3A, 4A, and 5A has a similarconfiguration to that of implant 100 of FIG. 1, except that it hasportions of its perimeter flattened or truncated so as to have atruncated medial side 117′ and truncated lateral side 119′. As bestshown in FIGS. 3A and 5A, medial side 117′ is truncated to a greaterextent than lateral side 119′. Alternatively, the medial side 117′ couldbe truncated to a lesser extent than lateral side 119′. FIG. 3B shows anembodiment of the present invention with implant 100″ having medial side117″ truncated to approximately the same extent as lateral side 119′.

[0111] Implant 100′ has a major diameter or height equal to the distancebetween bone-engaging projects 118′ on opposed arcuate portions 104′,108′. The width of implant 100′ is equal to the distance between aflattened segment and a point diametrically opposite the flattenedsegment, such as the distance between the medial side 117′ and lateralside 119′. The effect of having at least one of medial side 117′ andlateral side 119′ truncated or reduced is that the width of implant 100′is substantially reduced while the major diameter or height of implant100′ is maintained.

[0112]FIGS. 13A and 17 show a pair of side-by-side implants 100′ havinga truncated medial side 117′ and a pair of side-by-side implants 300′having a truncated medial side 317′ and a truncated lateral side 319′,respectively. The implants are implanted across the disc space with themedial sides facing and adjacent to another implant such that thecombined overall width of the two spinal implants is less than twice themajor diameter or height of the implants.

[0113] Shown in FIGS. 14-16, in accordance with the present invention,as embodied and broadly described herein, is an embodiment of anexpandable push-in artificial interbody spinal fusion implant 200 forposterior insertion across a disc space D between two adjacent vertebralbodies V of a human spine. Push-in implant 200 of the present inventionincludes an upper member 202 having an arcuate portion 204 adapted forplacement toward and at least in part within the upper of the adjacentvertebral bodies V and a lower member 206 having an arcuate portion 208adapted for placement toward and at least in part within the lower ofthe adjacent vertebral bodies V.

[0114] As shown in FIG. 14, implant 200 may be angled or tapered so asto converge from trailing end to leading end when in the collapsedposition for insertion into the spine. The taper on implant 200 mayfacilitate its insertion. Alternatively, as shown in FIG. 14A, theimplant of the present invention may be angled or tapered so as todiverge from trailing end to leading end when in the collapsed positionfor insertion into the spine. For an implant with an angle that divergesfor trailing end to leading end, the leading end may have a chamfer orother configuration to reduce the size of the leading end to facilitateinsertion of the implant into the spine.

[0115] Implant 200 in FIGS. 14 and 15 is shown being implanted into thespine from the posterior aspect with expander 222 on the distal end 226or leading end 250 of implant 200. While anterior and posterior aspectapproaches have been illustrated herein, the present invention is notlimited to these illustrated approaches. In particular, but not limitedthereto, the push-in implant of the present invention also may be usedin push-in implants for insertion from the translateral aspect of thespine as disclosed by Michelson in U.S. Pat. No. 5,860,973, which isincorporated herein by reference.

[0116] As best shown in FIG. 16, tracks 232, 234 of upper and lowermembers 202, 206 of the second embodiment have a cooperating surface 266and expander 222 has a corresponding cooperating surface 268 thatcontacts cooperating surface 266 of tracks 232, 234 to orient expander222 in a predetermined location. The cooperating surfaces orientexpander 222 within implant 200 such that the axis of rotation ofexpander 222 is parallel to the longitudinal axis of implant 200 andmore particularly center expander 222 within implant 200 such that theaxis of rotation of expander 222 coincides with longitudinal axis L ofimplant 200.

[0117] Tracks 232, 234 include sides 270 having cooperating surface 266and expander 222 has corresponding cooperating surface 268 used toorient expander 122 in a predetermined location. Cooperating surface 266of side 270 is a detent and corresponding cooperating surface 268 ofexpander 222 is a projection. The projection preferably projects awayfrom expander 222 in a direction parallel to the longitudinal axis ofimplant 200. The detent and the projection preferably center expander222 within implant 200 such that the axis of rotation of expander 222coincides with the longitudinal axis of implant 200.

[0118] Shown in FIGS. 17-19, in accordance with the present invention,as embodied and broadly described herein, are three more embodiments ofan expandable push-in artificial interbody spinal fusion implant 300 forinsertion across a disc space D between two adjacent vertebral bodies Vof a human spine. Push-in implant 300 of the present invention includesan upper member 302 having an arcuate portion 304 for orientation towardthe upper of adjacent vertebral bodies V and a lower member 306 havingan arcuate portion 308 for orientation toward the lower of the adjacentvertebral bodies V.

[0119] Implant 300 of the present embodiment may include any of thevarious features disclosed in association with implant 100 and implant200 disclosed herein. Implant 300 further includes a side surface 372contoured to cooperatively receive another implant. See U.S. Pat. No.5,593,409 by Michelson for a discussion of the advantages associatedwith placing implants in side-by-side contact.

[0120] Another aspect of implant 300 is that its upper and lower members302, 306 have screw holes 374 passing therethrough adapted to receive ascrew 378 passing from the interior of implant 300 into adjacentvertebral bodies V to anchor implant 300 to an adjacent vertebral bodyV.

[0121] The articulation may be of one of two general types, examples ofwhich are each herein disclosed. As shown in previously describedembodiments of the present invention, the articulation may allowrotation about the articulation. A second type of articulation allowsfor both rotation and expansion at the point of articulation. An exampleof this is shown in FIG. 19, where a peg and hook design is utilized. Inthis example both functions, that is, rotation or pivoting, and capturedor limited expansion with a fixed end point or stop, occur at the samelocation. Alternatively, and without departing from the teachings of thepresent invention, those functions can be divided. By way of exampleonly, and not limitation, expansion can be allowed and controlled by aninterlocking wall design, as shown by the interlocking members in thealternative embodiments of FIGS. 20 and 21. Various other structuralfeatures as would be obvious to one of ordinary skill in the art afterthe teachings herein can similarly be employed.

[0122] A fixed end point for the implant expansion is preferred for theproper functioning of the opposed bone screws. A purpose of the opposedbone screws is to rigidly secure the implant within the vertebralsegment. A further purpose is to pull each of the adjacent vertebralbodies toward the implant and towards each other so as to have aconstruct resistant to the deleterious effects of vertebral rocking asmay otherwise occur with spinal flexion and extension absent suchrestraint. If the articulation device captured the upper and lowermembers together, as in the embodiments of FIGS. 1-16, by closelyencircling a post then the implant could not expand at that location. Sothe coupling mechanism of FIG. 19 permits the upper and lower members toremain articulated, permits the implant to expand, and permits thescrews to pull against the implant and each other, in oppositedirections and to pull the bones toward each other. The optionalextended slot and peg configuration on the right-hand side of FIG. 19illustrated in dashed image lines is not needed to hold the implanttogether.

[0123] In accordance with this embodiment of the present invention, asecond expander may be located at least in part between the upper andlower members for moving at least a portion of the upper and lowermembers away from one another to increase the height of the implantdefined by the maximum distance between the arcuate portions of theupper and lower members. All of the features described herein for theexpander may also be applicable to the second expander. Additionally,the second expander may be located proximate an end of the implantopposite the other expander, thereby providing an implant capable ofbeing expanded at both ends of the implant. The increased height of theimplant resulting from moving the two expanders may be the constant orvaried along the length of the implant according to the desiredconfiguration of the implant.

[0124] The expandable push-in spinal fusion implant may be made ofartificial or naturally occurring materials suitable for implantation inthe human spine. The implant can comprise bone including, but notlimited to, cortical bone. The implant can also be formed of materialother than bone, such as metal including, but not limited to, titaniumand its alloys or ASTM material, surgical grade plastics, plasticcomposites, ceramics, or other materials suitable for use as a push-inspinal fusion implant. The plastics may be bioresorbable. The push-inspinal fusion implant of the present invention can further be formed ofbone growth promoting materials, including but not limited to, bonemorphogenetic proteins, hydroxyapatite, and genes coding for theproduction of bone. The push-in implant can be treated with a bonegrowth promoting substance, can be a source of osteogenesis, or can beat least in part bioabsorbable. The push-in implant of the presentinvention can be formed of a porous material.

[0125] The expandable push-in spinal fusion implant of the presentinvention may be coated with, comprised of, be used in combination with,or have a hollow for containing bone growth promoting materials,including but not limited to, bone morphogenetic proteins,hydroxyapatite, and genes coding for the production of bone. The push-inspinal fusion implant of the present invention can be formed of amaterial that intrinsically participates in the growth of bone from oneof adjacent vertebral bodies V to the other of adjacent vertebral bodiesV.

[0126] While various embodiments of the present invention are presentedby way of example only and not limitation, common to each of them, isthat the expandable push-in spinal fusion implant adapted for linearinsertion across disc space D between two adjacent vertebral bodies V ofa human spine has an upper member having an arcuate portion adapted forplacement toward and at least in part within the upper of the adjacentvertebral bodies V. The implant also has a lower member having anarcuate portion adapted for placement toward and at least in part withinthe lower of the adjacent vertebral bodies V. The arcuate portions ofthe upper and lower members have at least one opening. The openings ofthe upper and lower members are in communication with one another topermit for the growth of bone from vertebral body V to adjacentvertebral body V through the implant. On the exterior of each of theopposed arcuate portions of the upper and lower members is at least aportion of a bone-engaging projection adapted for linear insertion. Ablocker in the form of an expander preferably is located proximate atleast one of the ends to hold at least a portion of the upper and lowermembers apart from one another to increase the implant height.Applicant's U.S. patent application Ser. No. 09/612,188, filed Jul. 7,2000 is hereby incorporated by reference in the entirety.

[0127] There is disclosed in the above description and the drawingsimplants, which fully and effectively accomplish the objectives of thisinvention. However, it will be apparent that variations andmodifications of the disclosed embodiments may be made without departingfrom the principles of the invention or the scope of the appendedclaims.

What is claimed is:
 1. A push-in interbody spinal fusion implant for atleast in part linear insertion across the surgically corrected height ofa disc space between two adjacent vertebral bodies of a spine, saidimplant comprising: an upper member having a portion being at least inpart arcuate adapted for placement toward and at least in part withinone of the adjacent vertebral bodies, said upper member having at leastone opening adapted to communicate with one of the adjacent vertebralbodies, said upper member having a proximal end and a distal end; alower member having a portion being at least in part arcuate adapted forplacement toward and at least in part within the other of the adjacentvertebral bodies, said lower member having at least one opening adaptedto communicate with the other of the adjacent vertebral bodies, saidopenings of said upper and lower members being in communication with oneanother and adapted for permitting for the growth of bone from adjacentvertebral body to adjacent vertebral body through said implant and beingsufficiently sized and located to allow for interbody spinal fusionthrough said implant, said lower member having a proximal end and adistal end corresponding to said proximal end and said distal end ofsaid upper member, respectively, and a length between said proximal anddistal ends, said upper and lower members articulating therebetweenadjacent one of said proximal ends and said distal ends of said upperand lower members and allowing for expansion of the height of saidimplant, said upper and lower members having a first position relativeto one another allowing for a collapsed implant height during insertionof said implant into the spine and a second position relative to oneanother allowing for an increased height, said arcuate portions of saidupper and lower members in the first position being angled to oneanother over a substantial portion of the length of said implant andforming at least a portion of one of a frusto-conical shape and theshape of a cylinder split along a horizontal plane through itsmid-longitudinal axis with said upper member and said lower member beingangled to each other along the length of said implant; at least aportion of a bone-engaging projection is adapted for linear insertionformed on the exterior of each of said opposed arcuate portions of saidupper and lower members for penetrably engaging the adjacent vertebralbodies and to facilitate securing said implant into the spine; and atleast one blocker adapted to cooperatively engage and hold at least aportion of said upper and lower members apart so as to maintain theincreased height of said implant and resist the collapse of said implantto the collapsed implant height when said implant is in a final deployedposition.
 2. The push-in implant of claim 1, further comprising a hollowdefined between said upper and lower members in communication with saidopenings in each of said upper and lower members, said hollow beingadapted to receive fusion-promoting substances.
 3. The push-in implantof claim 2, wherein said hollow has a width that is unobstructed by anymechanism for moving said blocker.
 4. The push-in implant of claim 2,further comprising a second hollow between said upper and lower memberslocated between said blocker and said end of said implant proximate saidblocker.
 5. The push-in implant of claim 3, wherein said implant has aconstant width in both the collapsed height and the increased height. 6.The push-in implant of claim 3, wherein said blocker is located at leastin part between said upper and lower members.
 7. The push-in implant ofclaim 3, wherein said blocker is located proximate at least one of saidends of said upper and lower members.
 8. The push-in implant of claim 3,wherein said blocker is adapted to cooperatively engage a tool used tomove said blocker from an initial position to a final position toincrease the height of said implant, said tool not being a part of saidimplant and being removed from said implant after moving said blockerinto the final position.
 9. The push-in implant of claim 3, wherein saidimplant has a width and said blocker has a width less than the width ofsaid implant.
 10. The push-in implant of claim 3, wherein each of saidupper and lower members are adapted to cooperate with and to fixedlylocate said blocker.
 11. The push-in implant of claim 10, wherein eachof said upper and lower members have a track configured to permit saidblocker to seat therein.
 12. The push-in implant of claim 11, wherein atleast one of said tracks and said blocker are adapted to cooperate witheach other to center said blocker along a longitudinal axis of saidimplant.
 13. The push-in implant of claim 3, wherein said blocker movessaid arcuate portions of said upper and lower members from a firstangled orientation to a second angled orientation relative to oneanother.
 14. The push-in implant of claim 3, further comprising a secondblocker located between said upper and lower members for holding atleast a portion of the upper and lower members apart where said secondblocker is located.
 15. The push-in implant of claim 3, wherein saidblocker is an expander adapted to expand said implant from a firstcollapsed height to a second expanded height when moved from a first toa second position.
 16. The push-in implant of claim 15, wherein saidexpander is located proximate said proximal ends of said upper and lowermembers.
 17. The push-in implant of claim 15, wherein said expander islocated proximate said distal ends of said upper and lower members. 18.The push-in implant of claim 15, wherein said hollow is substantiallyunobstructed by said expander extending along a substantial portion ofthe length of said hollow so as to permit growth of bone from adjacentvertebral body to adjacent vertebral body through said implant.
 19. Thepush-in implant of claim 15, wherein said expander is adapted tocooperatively engage a tool used to move said expander from an initialposition to a final position to increase the height of said implant,said tool not being a part of said implant and being removed from saidimplant after moving said expander into the final position.
 20. Thepush-in implant of claim 15, wherein said expander is adapted tocooperatively engage a tool that rotates about an axis parallel to thelongitudinal axis of said implant to rotate said expander to increasethe height of said implant.
 21. The push-in implant of claim 20, whereinsaid expander rotates in a plane perpendicular to the longitudinal axisof said implant to increase the height of said implant.
 22. The push-inimplant of claim 21, wherein said expander remains in the same locationalong the longitudinal axis of the implant when rotated.
 23. The push-inimplant of claim 15, wherein said expander moves said arcuate portionsof said upper and lower members from a first angled orientation to asecond angled orientation relative to one another.
 24. The push-inimplant of claim 15, wherein each of said upper and lower members areadapted to cooperate with said expander.
 25. The push-in implant ofclaim 24, wherein each of said upper and lower members have a trackconfigured to permit said expander to rotate therein.
 26. The push-inimplant of claim 25, wherein said track of said upper member and saidtrack of said lower member are in the same plane.
 27. The push-inimplant of claim 25, wherein said track of said upper member and saidtrack of said lower member are parallel to one another.
 28. The push-inimplant of claim 25, where said track of said upper member and saidtrack of said lower member are in a plane perpendicular to thelongitudinal axis of said implant.
 29. The push-in implant of claim 15,wherein said upper and lower members structurally cooperate with saidexpander so as to keep said expander located within said implant. 30.The push-in implant of claim 25, wherein at least one of said tracks ofsaid upper and lower members has a cooperating surface, said expanderhaving a corresponding cooperating surface that contacts saidcooperating surface of said at least one track to orient said expanderin a predetermined location.
 31. The push-in implant of claim 30,wherein said cooperating surfaces orient said expander within saidimplant such that the axis of rotation of said expander is parallel withthe longitudinal axis of said implant.
 32. The push-in implant of claim31, wherein said cooperating surfaces center said expander within saidimplant such that the axis of rotation of said expander coincides withthe longitudinal axis of said implant.
 33. The push-in implant of claim3, wherein said upper and lower members are configured to cooperate withone another so as to stop said upper and lower members from being movedapart from one another more than a predetermined distance.
 34. Thepush-in implant of claim 24, wherein said upper and lower members areadapted to cooperate with said expander so as to center said expanderwithin a cross section of the upper and lower members.
 35. The push-inimplant of claim 25, wherein at least one of said tracks of said upperand lower members includes at least one side having a cooperatingsurface, said expander having a corresponding cooperating surface thatcontacts said cooperating surface of said at least one side to orientsaid expander in a predetermined location.
 36. The push-in implant ofclaim 35, wherein said cooperating surface of said at least one side isa detent and said corresponding cooperating surface of said expander isa projection.
 37. The push-in implant of claim 36, wherein said detentand said projection center said expander within said implant such thatthe axis of rotation of said expander coincides with the longitudinalaxis of said implant.
 38. The push-in implant of claim 15, wherein saidexpander has a first height corresponding to the height of said expanderwhen said implant is initially inserted into the spine, said expanderhaving a second height corresponding to the height of said expander whensaid expander is moved into a final deployed position to increase theheight of said implant, said second height being greater than said firstheight.
 39. The push-in implant of claim 15, wherein said expander has adepth dimension less than that of said first and second height of saidexpander.
 40. The push-in implant of claim 39, wherein said expander hasa fixed shape during movement from an initial insertion position to afinal deployed position within said implant.
 41. The push-in implant ofclaim 15, further comprising a second expander located between saidupper and lower members for moving at least a portion of the upper andlower members away from one another to increase the maximum height ofsaid implant where said second expander is located.
 42. The push-inimplant of claim 41, wherein said second expander rotates to increasethe height of said implant.
 43. The push-in implant of claim 41, whereinsaid second expander is located proximate an end of said implantopposite said expander.
 44. The push-in implant of claim 41, whereinsaid implant has a longitudinal axis and said second expander rotates ina plane perpendicular to the longitudinal axis of said implant toincrease the height of said implant.
 45. The push-in implant of claim43, wherein said hollow is substantially unobstructed by said secondexpander extending along a substantial portion of the length of saidhollow so as to permit growth of bone from adjacent vertebral body toadjacent vertebral body through said implant.
 46. The push-in implant ofclaim 43, wherein said second expander remains in the same locationalong the longitudinal axis of the implant when rotated.
 47. The push-inimplant of claim 41, wherein said second expander is located proximateone of the proximal end and the distal end of said upper and lowermembers.
 48. The push-in implant of claim 47, wherein said hollow isunobstructed by said second expander extending along a substantialportion of the length of said hollow to permit growth of bone fromadjacent vertebral body to adjacent vertebral body through said implant.49. The push-in implant of claim 47, further comprising a second hollowbetween said upper and lower member located between said second expanderand said end of said implant proximate said second expander.
 50. Thepush-in implant of claim 41, wherein each of said upper and lowermembers have a track within which said second expander rotates.
 51. Thepush-in implant of claim 50, wherein said track is configured to permitsaid second expander to rotate therein and then to move from side toside within said track.
 52. The push-in implant of claim 41, whereinsaid second expander has a first height corresponding to the height ofsaid second expander when said implant is initially inserted into thespine, said second expander having a second height corresponding to theheight of said second expander when said second expander is moved into afinal deployed position to increase the height of said implant, saidsecond height being greater than said first height.
 53. The push-inimplant of claim 41, wherein said second expander has an upper surface,a lower surface, and side surfaces as defined when said second expanderis positioned to increase the height of said implant, and said sidesurfaces intersecting said upper and said lower surfaces at twodiametrically opposed junctions.
 54. The push-in implant of claim 53,wherein the difference between said first height and said second heightof said second expander approximates the difference in height of saidimplant between said first position and said second position as measuredproximate the location of said second expander.
 54. The push-in implantof claim 3, wherein said upper and lower members have walls contactingone another.
 56. The push-in implant of claim 54, wherein said walls arealigned parallel with the longitudinal axis of said implant.
 57. Thepush-in implant of claim 54, wherein said walls are at least in partoverlapping.
 58. The push-in implant of claim 3, wherein said upper andlower members have a rotational articulation therebetween adjacent oneof said proximal end and said distal end of said upper and lowermembers.
 59. The push-in implant of claim 58, wherein said rotationalarticulation is at one of said proximal end and said distal end of saidupper and lower members opposite said blocker.
 60. The push-in implantof claim 58, wherein said rotational articulation allows for expansion.61. The push-in implant of claim 60, wherein said rotationalarticulation allows for limited expansion.
 62. The push-in implant ofclaim 3, wherein one of said upper and lower members has an interiorwall, which is unexposed, extending therefrom toward the other of saidupper and lower members when said implant is in an initial insertionposition, and when said implant is in a final position said implant hasa shape such that each of said arcuate portions of said upper and lowermembers are separated by at least a portion of said interior wall, whichnow has an exposed side.
 63. The push-in implant of claim 62, whereinsaid upper and lower members have side walls for engaging each other.64. The push-in implant of claim 63, wherein said side walls of saidupper and lower members are at least partially overlapping walls. 65.The push-in implant of claim 62, wherein said arcuate portions of saidupper and lower members form an angular orientation relative to oneanother when said implant is in the final position.
 66. The push-inimplant of claim 62, wherein said arcuate portions of said upper andlower members when said implant is in the final position form one of afrusto-conical shape and the shape of a cylinder split along ahorizontal plane through its mid-longitudinal axis with said uppermember and said lower member being angled to each other.
 67. The push-inimplant of claim 3, wherein said implant has an interior, at least oneof said upper and lower members has a screw hole passing therethroughadapted to receive a screw passing from said interior of said implantinto one of the adjacent vertebral bodies.
 68. The push-in implant ofclaim 67, wherein each of said upper and lower members has at least onescrew hole passing therethrough adapted to receive a screw passing fromsaid interior of said implant into the adjacent vertebral body incontact with each of said upper and lower members respectively.
 69. Thepush-in implant of claim 67, further comprising at least one screwadapted to pass from said interior of said implant through said screwhole and into the adjacent vertebral body to anchor said implant to theadjacent vertebral body.
 70. The push-in implant of claim 3, whereinsaid implant has a side surface when in a final position that iscontoured to cooperate with another implant.
 71. The push-in implant ofclaim 70, wherein said implant and said cooperating other implant have acombined width therebetween less than the combined height of saidimplant and said cooperating other implant.
 72. The push-in implant ofclaim 3, further comprising a cap for closing one of said proximal endand said distal end of said upper and lower members, said cap having anexterior surface and an interior surface.
 73. The push-in implant ofclaim 72, wherein said interior surface of said cap has spaced slotsabout its circumference to facilitate a snap fit of said cap into saidimplant.
 74. The push-in implant of claim 3, wherein said implantcomprises an artificial material other than bone.
 75. The push-inimplant of claim 3, wherein said implant is made of an artificialmaterial that is stronger than bone.
 76. The push-in implant of claim 3,wherein said implant is made of an artificial material that is harderthan bone.
 77. The push-in implant of claim 3, wherein said implantcomprises bone.
 78. The push-in implant of claim 77, wherein said boneincludes cortical bone.
 79. The push-in implant of claim 3, wherein saidimplant comprises bone growth promoting material.
 80. The push-inimplant of claim 79, wherein said bone growth promoting material isselected from the group consisting of bone morphogenetic protein,hydroxyapatite, and genes coding for the production of bone.
 81. Thepush-in implant of claim 3, wherein said implant is treated with a bonegrowth promoting substance.
 82. The push-in implant of claim 3, whereinsaid implant is a source of osteogenesis.
 83. The push-in implant ofclaim 3, wherein said implant is at least in part bioabsorbable.
 84. Thepush-in implant of claim 3, wherein said implant comprises metal. 85.The push-in implant of claim 84, wherein said metal is ASTM materialsuitable for use in said push-in spinal fusion implant.
 86. The push-inimplant of claim 84, wherein said metal includes titanium.
 87. Thepush-in implant of claim 3, wherein said implant comprises a plasticmaterial.
 88. The push-in implant of claim 3, wherein said implantcomprises a ceramic material.
 89. The push-in implant of claim 3,wherein said implant is formed of a porous material.
 90. The push-inimplant of claim 3, wherein said implant is formed of a material thatintrinsically participates in the growth of bone from adjacent vertebralbody to adjacent vertebral body through said implant.
 91. The push-inimplant of claim 3, wherein at least a portion of said implant istreated to promote bone ingrowth between said implant and said adjacentvertebral bodies.
 92. The push-in implant of claim 3, in combinationwith a chemical substance to inhibit scar formation.
 93. The push-inimplant of claim 3, wherein said blocker is an expander having anexternal thread, each of said upper and lower members having a threadedconverging portion adapted to cooperate with said external thread ofsaid expander to expand said implant from a first collapsed height to asecond expanded height when said expander is rotated from a first to asecond position.
 94. The push-in implant of claim 79, wherein said bonegrowth promoting material includes at least one of bone, bonemorphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 95. The push-in implant of claim 1, further incombination with a bone growth promoting material.
 96. The push-inimplant of claim 95, wherein said bone growth promoting materialincludes at least one of bone, bone morphogenetic protein,hydroxyapatite, and genes coding for the production of bone.